A first group of this invention relates to a biodegradable sustained-release preparation.
In recent years, sustained release of an active ingredient has attracted attentions in various fields. For example, there are an aromatic which imparts refreshing taste to the air in a room and as a pest controlling means, a mating disruption agent making use of a sex pheromone and an attracting insecticide in which the mating disruption agent and insecticide are used in combination.
These agents are required to have durable effects for a long period of time so that an excellent technique for sustained release is necessary. Recently, they are desired to have biodegradability in addition.
For example, a mating disruption agent, attracting insecticide or the like used for agricultural purposes is hardly collected after use and most of them are left alone in the upland field or the like. Because, collection of such an agent, which has been distributed in a large amount, after application requires many hands and is therefore substantially impossible. The aromatic used indoors is disposed as rubbish. Since plastic waste matters generate much heat at the time of incineration, thereby damaging an incinerator, they are often buried in the ground. Accordingly, there is a demand for a biodegradable type sustained-release preparation which can be degraded by microorganisms at the time when buried in the ground and does not remain in the soil.
In recent years, various materials having biodegradability have been proposed and some of them have already been industrialized. They can be classified into some groups from the viewpoint of the raw material constituting them. Examples include cellulose type, starch-added type, aliphatic polyester type and polyvinyl alcohol type. They are used suitably in consideration of their characteristics such as applications or price, however, an aliphatic polyester type is preferred for the sustained release of an active ingredient.
For the agricultural applications where an agent tends to be left alone in the field after application, described in Japanese Patent Application Laid-Open No. 6-116103 is a pest controlling agent comprising a biodegradable aliphatic polyester and an active ingredient. The present inventor has already developed, as a sustained-release pheromone preparation having biodegradability, a sustained-release pheromone preparation comprising as a sustained-release layer, a polymer composed mainly of 3-hydroxybutyric acid (Japanese Patent Application Laid-Open No. 5-163110).
As described above, an aliphatic polyester type preparation is used preferably as a sustained-release preparation having biodegradability. In the aliphatic polyester, however, molecular chains are firmly bonded statically through an ester linkage in its structure, which makes it difficult for the active ingredient to diffuse the gap of the polymer segment, resulting in small transmittance of the active ingredient through the aliphatic polyester. The aliphatic polyester is therefore accompanied with the problem that a release surface area should be widened in order to increase the transpiration amount of the active ingredient or a number of sustained release preparations should be placed in order to secure a certain concentration.
A second group of the present invention relates to a biodegradable pheromone dispenser.
In recent years, as a pest controlling means, a controlling method making use of a pheromone has attracted attentions because it is safe and besides, it does not impart the pest insects with resistance.
A pheromone dispenser is requested to release a pheromone stably for a long period of time in order to deal with the breeding of pest insects over a breeding season and is also requested to have applicability to crops or other things to be treated. Various pheromone dispensers equipped with both excellent release performance and easy applicability have therefore been proposed.
The pheromone dispensers so far proposed can be classified into three types based on their shapes. The first one is a microcapsule or hollow fiber type used for distribution. The second one is a matrix type wherein a pheromone has been dispersed in a polymeric material. The third one is a so-called reservoir type in which a pheromone has been held as a liquid. The microcapsule or hollow fiber type can be applied easily by distribution or the like but involves a problem such as short control period. The matrix type is accompanied with the problem that the release rate of a pheromone depends on the pheromone concentration in the polymeric material so that the release rate inevitably shows a gradual decrease. Accordingly, as a pheromone dispenser, the reservoir type whose intra-membrane concentration gradient does not change so much has been rated high because of stable release performance over a long period of time.
It is however the present situation that most of such pheromone dispensers are not collected after application to the field such as upland field and are left alone in the field.
There has accordingly been a demand for a biodegradable type pheromone dispenser which is degraded in the soil and does not remain in the field and various proposals have already been made.
For example, in Japanese Patent Application Laid-Open No. 6-116103, a pest controlling agent made of a biodegradable aliphatic polyester is described. Described are a spherical pest controlling agent wherein the surface of an active ingredient in the form of a microcapsule has been covered with a biodegradable polymeric material; a spherical-, film- or ribbon-shaped material obtained by dispersing an active ingredient in a biodegradable polymeric material and then forming or molding the resulting dispersion; a film-shaped material having a barrier layer on its surface; and an adhesive-layer-having agent permitting easy application. Also described in it is a method of encapsulating an active ingredient in a capillary-shaped tube and releasing an active ingredient from the opening portion of the capillary tube. It is however difficult to secure stable release over a long period of time by such pest controlling agents.
As describe above, the present inventor has already proposed (Japanese Patent Application Laid-Open No. 5-163110) a sustained-release pheromone preparation using, as a sustained-release layer, a polymer composed mainly of 3-hydroxybutyric acid. Use of this polymer however requires a decrease in the thickness of the sustained-release layer or an increase in the release surface area, because this polymer has a small transmittance rate of a pheromone.
As such, a polyester is a substance having a small transmittance of pheromones and is not suited for use as a material for a reservoir type pheromone dispenser. Described specifically, aromatic polyesters such as polyethylene terephthalate hardly transmits pheromones. Aliphatic polyesters are not always same in the transmittance of pheromones. Under such situations, the kind and thickness of the aliphatic polyester appropriate for a sustained-release layer of a reservoir type pheromone dispenser having both biodegradability and sustained release property of pheromones have not yet been made cleared.
A third group of the present invention relates to a biodegradable pest controlling agent.
There are various methods to control harmful microorganisms which cause damage to field crops or horticultural crops. As described above, mating disruption agents and attracting insecticides making use of the sex pheromone of an insect have recently drawn attentions as excellent controlling means from the environmental viewpoint.
A variety of such controlling agents have been proposed and some of them have already been industrialized. Examples include, as described above, a polyethylene-made capillary tube or container made of an ethylene-vinyl acetate copolymer encapsulating an active ingredient; a polyvinyl chloride sheet having an active ingredient kneaded therein; a hollow fiber having an active ingredient enclosed therein; and a polyvinyl chloride sheet, which has an active ingredient kneaded therein, cut into small pieces to permit aerial application. It is the present situation that most of such agents are not collected after application and are left alone in the field.
There is accordingly a demand for a biodegradable pest controlling agent which is degraded in the soil and does not remain in the field.
As described above, the present inventor has proposed a biodegradable sustained-control pheromone preparation using, as a sustained-release layer, a polymer mainly composed of 3-hydroxybutyric acid in Japanese Patent Application Laid-Open No. 5-163110. Use of this polymer however requires a decrease in the thickness of the sustained-release layer or an increase in the release surface area, because this polymer has a small transmittance rate of pheromone. In addition, it is accompanied with the inconvenience that the shape of the controlling agent, for example, bag shape is not suited for aerial application.
In addition, a pest controlling agent made of a biodegradable aliphatic polyester is proposed in Japanese Patent Application Laid-Open No. 6-116103, in which an active ingredient dispersed in a biodegradable polymeric material and then formed into a spherical, film or ribbon-shaped agent is described. In order to disperse the active ingredient in the biodegradable aliphatic polyester, however, a cumbersome step such as film formation using a solvent is necessary. Moreover, the above agent is accompanied with the drawback that the active ingredient dispersed in a biodegradable aliphatic polyester having low affinity therewith tends to cause bleeding without a further treatment.